Telecommunications system

ABSTRACT

Virtual dedicated voice connections between parties  18, 19  to a packet switched system can be created by reserving capacity for such connections in the packet switched system. The capacity reservable by any one party is limited, to prevent oversubscription of resources in the packet switched. The system incorporates a call admission control processor  12, 17  for controlling access to the packet switched call routing system such that a voice call attempt is successful only if capacity for such a dedicated connection has previously been reserved. 
     The capacity reserved for the virtual connections is made available for use by other traffic when not required for voice calls.

This invention relates to telecommunications systems, and in particular to the provision of dedicated connections between defined points.

Modern telecommunications systems allow almost any telecommunications device to be connected to any other using conventional switched networks (circuit switched or packet switched).

Early attempts to integrate voice and data systems relied on carrying digital data over a circuit-switched system initially designed for analogue signals, in particular voice. Conversely, modern packet-switched telecommunications systems, such as those running under the “Internet Protocol”, are configured for digital data, and analogue data, notably voice, has to be adapted to fit the protocol. Voice, in particular, has rather different requirements from those of data. Small values of latency (delay) are much more significant to a human listener than they are to a machine processing incoming data. Jitter—the variability of the delay—is even more significant. Conversely, the amount of redundancy in human speech is such that a human listener can still comprehend a voice signal that has suffered impairment to a much greater degree than would be acceptable in a data signal.

Existing “Voice over Internet Protocol” systems have procedures in place to reflect these different priorities, but call quality can still fall below that expected on a switched circuit, in particular because in a packet-switched system, unlike a conventional circuit-switched call, resources are shared and the underlying connection requirements are “best effort”. Contention for resources, for example between a number of simultaneous voice calls, can result in insufficient bandwidth being available to support the call traffic required. In comparison, provided a line is available, a circuit-switched system dedicates capacity dedicated solely to a single connection for the duration it is required.

The problems of latency and of contention with other subscribers for bandwidth, mean that dedicated point-to-point links are still preferred for certain applications. Such dedicated point-to-point physical circuits are expensive to provide as they require dedicated infrastructure to be installed over the entire length of the link, and there are few synergies available to reduce the cost of installing several such links. They are also less robust to system failure, and replacement or diversion (whether in an emergency or otherwise) requires major re-installation work.

The present invention addresses these issues by providing a method of creating virtual dedicated connections between parties to a packet switched system by reserving capacity for such connections in the packet switched system. The invention also provides a packet switching system comprising means for reserving capacity for virtual dedicated connections between parties to the packet switched system. The dedicated connections may be reserved for voice traffic, and the system may be arranged that voice traffic can only be routed except by way of these dedicated links.

The packet-switched system preferably operates under the “Internet Protocol” and is either a private or limited-user system: such systems are known as Intranets and Extranets respectively. They have many of the characteristics of the public “Internet”, and indeed usually interface with it, but they make use of dedicated resources and normally have access controls such as “firewall” systems to prevent unauthorised access.

The invention extends to a call admission control process for controlling access to a packet switched call routing system in which, when a call is set up between a first party and a second party, the call is placed only if a dedicated link between a first party and a second party has previously been created.

Unlike a normal leased line, the capacity on the virtual connections according to the invention may be made available for use by other traffic when not required for the purpose for which it is reserved. Moreover, as the virtual dedicated connection is carried over a packet switched system, it is easy to reconfigure should it become necessary, for example because of relocation of either party to the connection, or of any intermediate part of the link.

One aspect of the present invention provides a call admission control processor for controlling access to a packet switched call routing system in which when a call is set up between a first party and a second party and the admission control layer allows the call to be placed only if connection between a first party and a second party has previously been allocated a predetermined capacity in the system, the allocation process itself being arranged such that allocation is only permitted to be set up if capacity between the called parties can be reserved without oversubscription of the resources in the routing system.

By establishing in advance which connections may be authorised, oversubscription can be avoided. Users may establish calls to two or more other parties at once, provided each individual connection has been authorised.

The capacity reservable by any one party may be limited to prevent oversubscription of the resources in the routing system. To ensure capacity is not reserved unnecessarily, establishment of an authorised connection may require the co-operation of both parties.

The amount of bandwidth (capacity) reserved for an individual connection may be selected depending on factors such as the quality of the link required, and the speed or other characteristics of the users' terminal equipment.

A connection may be to a dynamic location—for example connection may be made to a user's fixed or mobile terminal depending on factors such as time of day of the user's forwarding settings.

An embodiment of the invention will now be described by way of example only, with reference to the drawings, in which

FIG. 1 is a schematic illustration of an installation including a call admission control layer according to the invention.

FIG. 2 is a schematic illustration of a user terminal configured to be used with the invention.

FIG. 3 is a flow diagram illustrating the process by which capacity may be reserved.

FIG. 4 is a flow diagram illustrating the process by which a user may register with the system.

FIG. 5 is a flow diagram illustrating the process by which reserved capacity may be used to connect a voice call.

Referring to FIG. 1, the system illustrated comprises a registration processor 15 and a session authorisation processor 16. The registration processor 15 controls access to the system, and the session authorisation processor 16 controls the reservation of capacity.

Access to the system for reservation purposes is made by a user terminal 18, 19 through a user portal 10, whilst calls are set up through a session border controller 17. (For brevity, the users will be referred to by the same reference numerals as the respective terminals 18, 19 they are using).

The capacity reservation process will now be discussed, with reference to FIG. 3. A capacity store 13 maintains the details of all the reserved-capacity connections. It also stores details of the source and destination URIs (universal resource indicator) for each end of the established connections, together with the sample interval and codecs used. These latter factors determine the capacity (bandwidth) required to maintain a speech-quality link. When a user first subscribes to the system a specified amount of bandwidth is configured (several hundred kilobits/sec), which can be broken down into call slot reservations.

Once a user is identified to the system, he may request a virtual reserved-capacity connection to another party 19. The user 18 identifies the other party using a directory facility, for example by email address. This identity is sent by way of the portal 10 to the session authorisation processor 16 (step 33) which checks with the capacity store 13 whether there remains sufficient unallocated capacity to make the new allocation (step 34). It should be noted that the assessment is based on the capacity not allocated to virtual links, and not on the capacity allocated to such links but not currently in use.

If sufficient capacity is available—that is to say, sufficient capacity from the user's allocation remains available, a message is sent to the other party 19 (step 35) to request authorisation of this capacity for the new virtual link. The other party may accept such a link, in which case it will be added to the store of authorised connections 13 (step 36). The other party may, instead, decline. This may be done if, for instance, the other party has a large number of such connections established already and has insufficient remaining capacity for the newly-requested link.

If the link is accepted, network capacity is reserved for “Voice over Internet Protocol” (VoIP) calls between these two parties 18, 19. The data is then replicated to the network server 12 (step 37) so that connections can be made using the reserved capacity, and confirmation sent to both users 18, 19 (steps 38, 39). As this is a virtual connection over a packet switched network, when no such call is in progress the reserved capacity is available for other purposes, such as carrying less time-critical non-voice traffic. The speed with which such traffic can be carried will depend on how much of the capacity reserved for voice links is actually required at any given moment.

When capacity is reserved for a dedicated virtual link, a representation of the new link's availability is generated for display on both users' user displays. In response to the notifications 38, 39. Each user's terminal 18, 19 is configured to facilitate connection to the other's URI. As shown in FIG. 2, this can be done by allocating a button 22 on the control panel of a user device, and an associated indicator light 21, to the new link. Alternative user interfaces may be used, for example an icon or a pop-up on a computer screen, which can be activated by moving a cursor over it using an user input device such as a computer mouse. As another example, a standard Internet Protocol telephone may be used, one of the “soft keys” and the associated display being configured appropriately.

The user terminals are therefore configured to allow a user to readily establish calls with one or more of the parties with whom capacity has previously been reserved.

Registration with the system will now be discussed, with reference to FIG. 4. When a user connects to the system he accesses the SBC 17 through his terminal 18, 19 (step 30). The SBC 10 first corresponds with the authentication processor 15 (step 31) which checks the user name against a set of valid site IP addresses stored in the user identity store 11 for that user (step 32), and if the user is registering from a valid address, it then performs a password check. This ensures that any user attempting to use the system is indeed the user that he claims to be, and allows the SBC 10 to identify location information, specifically the IP address, currently associated with that user.

As shown in FIG. 5, when a user 18, having registered with the system wishes to establish a voice connection with a party 19 for which a dedicated link has previously been reserved, he operates the control 22 representing the called party, which causes the user terminal 18 to transmit a request 40 to the session border controller (SBC) 17 for a link to be set up to the terminal 19 currently associated with the URI specified in the request. The SBC 17 cooperates with the network server 12 (step 41) to establish this link. The network server 12 checks with the location database 14 for the current location (IP address) of the selected counterparty (step 42) and with the user identity database 11 to ensure the URIs and current locations of both the calling party and the called party are valid (step 43). If these checks are validated, the network server 12 generates a call attempt 44 to the user terminal 19 corresponding to the current IP address held for the called party. This causes the destination user's terminal 19 to generate an indication 21 that an incoming call is being made. If the called party wishes to accept the call, he activates the corresponding control 22 on his terminal 19 to transmit an authorisation 45 to the network server 12 which in turn transmits a instruction 46 to the session border controller 17 to establish the link (47, 48).

Either party 18, 19 may set up a call to the other, irrespective of which party initially reserved the capacity.

The network server 12 is arranged such that no VoIP call can be made unless the connection capacity has been previously reserved by the control system 16. When a customer 18 looks for a destination party 19 on the network the lookup process in the SBC 17 directs the user to the network server 12, which is configured so that the “voice” class of service can only be accessed this way.

The number of connections available to a customer is regulated by the authorisation server 16 to ensure that the total capacity of all the links available to a user 18 do not exceed the available bandwidth. Users can only provision within this authorised capacity. The entries in the database are policed to ensure that the user 18 setting up the call is using his own calling domain, and the target user 19 is always checked and consulted before the call is allowed. 

1. A method of creating virtual dedicated connections between parties to a packet switched system by reserving capacity for such connections in the packet switched system.
 2. A method according to claim 1, wherein the dedicated connections are reserved for voice traffic.
 3. A method according to claim 1, wherein reservation of capacity for a connection between two parties requires the co-operation of both parties.
 4. A method according to claim 1 wherein the capacity reservable by any one party is limited to prevent oversubscription of resources in the packet switched.
 5. Call admission control process for controlling access to a packet switched call routing system in which, when a call is set up between a first party and a second party, the call is placed only if a dedicated connection between a first party and a second party has previously been created according to the method of claim
 1. 6. Call admission control process according to claim 5, wherein voice calls are controlled such that they can only be connected if a dedicated connection has been reserved.
 7. A method according to claim 5 in which a user may establish calls to two or more other parties at once, each call using a dedicated link reserved by creating virtual dedicated connections between parties to a packet switched system by reserving capacity for such connections in the packet switched system.
 8. A method according to claim 5, wherein a network termination currently associated with an individual user identity is identified, and a dedicated link with the network termination so identified is established using capacity reserved for the user identity associated therewith
 9. A method according to claim 1, wherein the capacity reserved for the virtual connections is made available for use by other traffic when not required for the purpose for which it is reserved.
 10. A packet switching system comprising means for reserving capacity for virtual dedicated connections between parties to the packet switched system.
 11. A packet switching system according to claim 10, comprising means for reserving the dedicated connections for voice traffic.
 12. A packet switched telecommunications network according to claim 10, wherein the means for reserving capacity for a dedicated link is controlled by the co-operation of both parties to the link.
 13. A packet switched telecommunications network according to claim 10, comprising means for storing data relating to the dedicated links between individual parties, and further comprising means to limit the capacity reservable by any one party to prevent oversubscription of the resources in the network.
 14. A packet switched telecommunications network according to claim 10, comprising a call admission control processor for controlling access to the packet switched call routing system, the call admission control processor comprising means for receiving a request from a first party to set up a call to a second party, means for identifying whether capacity for a dedicated link between the first party and the second party has previously been reserved, and means for completing the connection if such capacity is reserved.
 15. A packet switched telecommunications system according to claim 14, wherein the call admission control processor comprises means for controlling voice calls such that they can only be connected over such a dedicated connection.
 16. A packet switched telecommunications system according to claim 14, wherein the call admission control processor comprises means to establish calls from a user to two or more other parties at once, each call using a dedicated connection.
 17. A packet switched telecommunications network according to claim 14, wherein the call admission control processor comprises location tracking means to identify a network termination currently associated with an individual user identity, and means for establishing a dedicated link with the network termination so identified using capacity reserved for the user identity associated therewith.
 18. A packet switched telecommunications network according to claim 10, further comprising means for allowing the capacity reserved for the virtual connections to be made available for use by other traffic when not required for the purpose for which it is reserved. 